The lead acid battery (LAB) industry represents more than $30B in annual sales globally. A common arrangement for LABs is to utilize lead oxide (PbO2) as a cathode, lead as an anode, and 2-8 M sulfuric acid as the electrolyte. Some features of LABs are: high discharge power, excellent high and low temperature operation, ultra-safe, and excellent existing recycling programs that are highly economical. However, LABs may utilize heavy metals that are or may become banned in the future due to toxicity and/or environmental concerns. For example, Europe threatens to extend the ban on heavy metals to lead acid batteries, including those used for vehicles. Further, in some applications, higher charge acceptance than current LABs provide may be desirable. For example, micro hybrid and stop/start technologies require higher charge acceptance that current lead acid battery technology cannot provide.
The charge acceptance problem in LABs is related to the negative electrode. As an example, the mechanism of LABs may include PbSO4 forming large crystals on the negative electrode. This leads to a sulfated negative electrode or a negative electrode that is at a lower state-of-charge than the positive. This failure mechanism is common in start-stop vehicles. Under the high-rate partial state-of-charge conditions that are required by mild/full hybrid electric vehicles, the lead electrode is known to suffer premature capacity loss due to aggressive sulfation at the electrode surface. The use of additives with high surface area alleviates this problem but does not eliminate it. This leads to a sulfated negative electrode or a negative electrode that is at a lower state-of-charge than the positive. This failure mechanism is common in start-stop vehicles.
Lead-carbon (PbC) batteries and UltraBattery® have been developed by several companies to address this challenge, which substitute activated carbon for the lead anode. Charge/discharge cycle testing of these batteries at 1C further confirmed that a standard positive electrode in an LAB could be charged and discharged at high rate. However, the negative electric double-layer capacitor-type electrode in the PbC battery had very low capacity and a capacitive voltage profile (i.e. sloping). Further, these batteries required a complicated negative electrode design that resulted in high resistance preventing adequate current for cold starting of vehicles.